EXPLAINER: What do we know about booster shots for COVID-19?

U.S. health officials may soon recommend COVID-19 booster shots for fully vaccinated Americans. A look at what we know about boosters and how they could help fight the coronavirus: WHY MIGHT WE NEED BOOSTERS?

It’s common for protection from vaccines to decrease over time. A tetanus booster, for example, is recommended every 10 years.

Researchers and health officials have been monitoring the real-world performance of the COVID-19 vaccines to see how long protection lasts among vaccinated people. The vaccines authorized in the U.S. continue to offer very strong protection against severe disease and death.

But laboratory blood tests have suggested that antibodies — one of the immune system's layers of protection — can wane over time. That doesn't mean protection disappears, but it could mean protection is not as strong or that it could take longer for the body to fight back against an infection.

The delta variant has complicated the question of when to give boosters because it is so much more contagious and much of the data gathered about vaccine performance is from before the delta variant was widely circulating. Delta is taking off at the same time that vaccine immunity might also be waning for the first people vaccinated.

Israel is offering a booster to people over 50 who were vaccinated more than five months ago. France and Germany plan to offer boosters to some people in the fall. The European Medicines Agency said it too is reviewing data to see if booster shots are needed.

WHEN WOULD THEY BE GIVEN?

It depends on when you got your initial shots. One possibility is that health officials will recommend people get a booster roughly eight months after getting their second shot of the Pfizer or Moderna vaccine.

Officials are continuing to collect information about the...